1. Field of the Invention
The present invention relates to a solution process for the homopolymerization of ethylene and the copolymerization of ethylene and butene-1 and especially to such a process in which there is a reduced tendency for isomerization of any butene-1 fed to the process. In particular the present invention relates to such reduction of isomerization in a solution polymerization process in which deactivated catalyst is not separated from the polymer.
2. Description of the Prior Art
Polymers of ethylene, for example, homopolymers of ethylene and copolymers of ethylene and higher alpha-olefins, are used in large volumes for a wide variety of end uses, for example, in the form of film, fibres, moulded or thermoformed articles, pipe, coatings and the like.
Processes for the preparation of, in particular, copolymers of ethylene and higher alpha-olefins are known. Such processes include processes in which the monomers are polymerized in the presence of a coordination catalyst, for example, a catalyst comprising a compound of a transition metal belonging to Groups IVB-VIB of the Periodic Table and an organometallic compound of a metal belonging to Groups I-IIIA of the Periodic Table.
A particularly preferred process for the polymerization of alpha-olefins is the high temperature or "solution" polymerization process, an example of which is described in Canadian Pat. No. 660 869 of A. W. Anderson, E. L. Fallwell and J. M. Bruce, which issued Apr. 9, 1963. In a solution process the process parameters are selected in such a way that both the monomer and polymer are soluble in the reaction medium. Under such conditions accurate control over the degree of polymerization, and hence the molecular weight of the polymer obtained, may be achieved, for example, by control of the reaction temperature. Solution processes are also disclosed in Canadian Pat. Nos. 1 171 065 of V. G. Zboril, M. A. Hamilton and R. W. Rees, and 1 171 066 of V. G. Zboril and M. A. Hamilton, both issued July 17, 1984, and 1 220 189 of M. A. Hamilton, D. A. Harbourne, C. G. Russell, V. G. Zboril and R. Mulhaupt, issued Apr. 07, 1987.
The polymerization reaction in a solution polymerization process is normally terminated by addition of a so-called "deactivator". A wide variety of compounds are capable of deactivating coordination catalysts, especially at the high temperatures used in a solution polymerization process. However, a deactivator must meet other, more stringent, criteria in order to be acceptable for use in a commercial process. If the deactivated catalyst remains in the polymer, the deactivator and deactivated catalyst residues must not cause problems in the separation of polymer from solvent and unreacted monomers, in the processing of the polymer obtained and in the resultant fabricated articles, and the polymer obtained must have commercially-acceptable colour, odour and toxicity properties. It is particularly difficult to predict the possible effects of a potential deactivator at the high temperatures of a solution process, especially with regard to isomerization of comonomers, degradation of the deactivator, generation of coloured species, reaction with antioxidants and other stabilizers and the like. Moreover, the behavior of the deactivator may be quite sensitive to changes in the operation of a solution process.
Deactivators for solution polymerization processes are known, for example, a fatty acid or an alcohol. The fatty acid is admixed with hydrocarbon solvent, normally the solvent of the polymerization process, and fed into the polymerization mixture, usually shortly after that mixture passes from the reactor. The polymerization mixture that has been treated with deactivator contains catalyst residues which may be removed by contacting the mixture with an adsorbent, for example, alumina. Such a deactivation and catalyst removal process is described in Canadian Pat. No. 732 279 of B. B. Baker, K. M. Brauner and A. N. Oemler, which issued Apr. 12, 1966.
Coordination catalysts containing vanadium may conveniently be deactivated by contacting the polymerization mixture with a solution of a salt of an alkaline earth metal or zinc and an aliphatic monocarboxylic acid dissolved in the hydrocarbon solvent used in the polymerization process. Such deactivation of coordination catalysts containing vanadium tends to result in polymer of improved colour, as is disclosed in Canadian Pat. No. 1 165 499 of V. G. Zboril, which issued Apr. 10, 1984. Titanium-based coordination catalysts used in a solution polymerization process may be deactivated to give polymer of improved colour by sequentially contacting the polymerization mixture with a minor amount of water and then with a solution of a salt of an alkaline earth metal or zinc and an aliphatic monocarboxylic acid dissolved in a hydrocarbon solvent, preferably the solvent used in the polymerization process, as is disclosed in Canadian Pat. No. 1 173 599 of M. A. Hamilton, D. A. Harbourne and V. G. Zboril, which issued Aug. 28, 1984.
The use of carbon dioxide and/or carbon monoxide to deactivate coordination catalysts is disclosed in U.S. Pat. No. 4,211,863 of M. P. McDaniel, J. D. Hottovy and M. B. Welch, which issued July 08, 1980, and in Japanese Patent Application No. 56/074 109 of Mitsubishi Petrochemical, published June 19, 1981. The use of a variety of deactivators, including water, esters, carbon dioxide, carbon monoxide and other organic compounds, to overcome difficulties associated with the use of alkali and/or alkaline earth metal salts of saturated fatty acids, aromatic carboxylic acids or zinc stearate in a high-pressure Ziegler polymerization process in disclosed in published European patent application No. 116 917 of Ruhrchemie, published Aug. 29, 1984.